i agree with to la bomb
how on earth did you get any triangles if you did what you said (extrude from a polygon plane), extrusions never make triangles

to fix that bumpy surface you could try the smooth brush in the sculpt geometry tool, it might actually be due to funny topology and a mix of soft and hard edges

come to think of it, you probably have those triangles because we you went mesh > cleanup and told it to make everything as triangles...